"I think this fall is very important," McCain said at a forum hosted by AFL-CIO and the Economic Policy Institute. "It's very important because we get into 2014 - the next election cycle. I think the issue really has ripened to the point that enough Americans are aware of it, we are either going to act or not act."

On PBS Monday, McCain said that if immigration reform is not passed, the Republican Party will never again win a national election.

"Let's say we enact it, comprehensive immigration reform - I don't think it gains a single Hispanic voter, but what it does, it puts us on a playing field where we can compete for the Hispanic voter," McCain told PBS' Gwen Ifill. "If we don't do that, frankly, I don't see - I see further polarization of the Hispanic voter and the demographics are clear that the Republican Party cannot win a national election. That's just a fact."

McCain compared the current system to "de facto amnesty because they are not leaving" and said that in his experience and from polls he's seen, most Americans support the pathway to citizenship as long as the undocumented pay a fine, learn English and get on the back of the line.

"It (immigration) has a broader spectrum of support than any I have ever seen in my political career," he said. He said that the broad range of groups and communities that support immigration reform "can galvanize" in the coming months to make passage a reality.

"We haven't done as an effective job as we are going to have to do between now and this vote," he said.

Rep. Xavier Becerra, D-Calif., agreed with McCain, adding that not only does he see reform passing, but passing with a pathway to citizenship.

"I firmly believe more than I have ever felt in the 20 years that I have been privileged to serve … that this is the year we are going to do it, as long as folks in the Capitol put country ahead of party," Becerra said. "I think if the bill the Senate passed a few weeks back were to be placed on the floor for a vote, it would pass bipartisan, today. We may end up working on a bill that's a House-derived version of immigration reform. But I think it will include the path to citizenship.

"If you recognize that everyone agrees we must tackle border security and it's good for our country, there is no reason why we shouldn't do something that's good for our economy, good for our country and finally, that lets millions of peoples … come out of shadows," he said.

Becerra added that they have been "trying" to give Speaker of the House John Boehner "the opportunity to open that door."

"At at the end of the day in the House, I think we see what the Senate saw: A chance to fix this broken immigration system in all of its aspects," he said.

McCain, the Arizona senator who consistently argues the border is already secure, conceded that the last minute addition of 20,000 new border patrol agents is unnecessarily costly and was a concession designed purely to gather more votes.

"We don't need 20,000 additional border control agents," he said. "What we do need is to use technology that has been developed, where we can survey the border more effectively … I voted for it so friends of mine would be comfortable we are securing the border. But the real securing the border is the technology as opposed to individuals."

He said that compared to 1986, when there were only 4,000 agents working the border, today's current 21,000 means the border is already more secure than the last time immigration reform was tackled.

"The border is more secure. And anybody who tells you it isn't I'd like to take them down and show them," he said.

The Republican senator even waded into the controversial remarks about DREAMers made by Rep. Steve King last week, calling his claims that for every valedictorian DREAMer there are 100 drug runner DREAMers with "calves the size of cantaloupes," "despicable rhetoric."

"I believe in America and I believe that at the end of the day we are going to do the right thing," he said. "We're not going to talk about people with cantaloupe calves, were not going to indulge, engage in that kind of despicable rhetoric … we are going to talk about the greatness of America."

Also today, more than 100 Republican donors sent a letter to Republican members of Congress urging immigration reform.

"We write to urge you to take action to fix our broken immigration system," the letter reads. It calls for securing the borders, providing a legal way for companies to hire legal workers and providing a path to "legal status."

A second letter from more than 400 members of industry, including the U.S. Chamber of Commerce, sent a letter to all members of the House also urging Congress "to enact legislation that would bring meaningful reforms to critical components of our nation's immigration system."

"Failure to act is not an option," the letter reads. "We can't afford to be content and watch a generation-old immigration system work more and more against our overall national interest."